An organic light-emitting device is a device in which a thin film containing a fluorescent organic compound is sandwiched between an anode and a cathode. In the device produces, an exciton of the fluorescent compound is produced by injecting an electron or a hole from each of the electrodes and the light radiated when the exciton returns to the ground state is utilized.
In a research by Eastman Kodak Company in 1987 (Appl. Phys. Lett. 51, 913 (1987)), there is reported a light emission of about 1,000 cd/m2 at an applied voltage of about 10 V for a device of separated-function two-layered structure using ITO for anode, a magnesium-silver alloy for cathode, respectively, an aluminum-quinolinol complex as an electron-transporting material, and a light-emitting material and a triphenylamine derivative as a hole transporting material. Related patents include U.S. Pat. No. 4,539,507; U.S. Pat. No. 4,720,432 and U.S. Pat. No. 4,885,211.
Light-emission from ultraviolet to infrared is possible by changing a kind of the fluorescent organic compounds and researches of various compounds therefor have been conducted actively recently. For example, they are described in U.S. Pat. No. 5,151,629; U.S. Pat. No. 5,409,783; U.S. Pat. No. 5,382,477; Japanese Patent Application Laid-Open No. H02-247278; Japanese Patent Application Laid-Open No. H03-255190; Japanese Patent Application Laid-Open No. H05-202356; Japanese Patent Application Laid-Open No. H09-202878 and Japanese Patent Application Laid-Open No. H09-227576.
Besides other than the organic light-emitting device using monomeric materials as described above, an organic light-emitting device using a conjugated polymer has been reported by a group of Cambridge University (Nature 347, 539 (1990)). In this report, the light-emission in a monolayer by forming a film of polyphenylenevinylene in a coating system is confirmed. The related patents on organic light-emitting devices using conjugated polymers include U.S. Pat. No. 5,247,190; U.S. Pat. No. 5,514,878; U.S. Pat. No. 5,672,678; Japanese Patent Application Laid-Open No. H04-145192 and Japanese Patent Application Laid-Open No. H05-247460.
Thus, recent progress in organic light-emitting devices is remarkable, and possibilities for a wide range of applications are indicated since it is characterized in that a thin and light-weight light-emitting device having high luminance at a low applied-voltage, diversity of light-emitting wavelength and high-speed response can be prepared.
However, there are numbers of problems in terms of durability such as the variation with time during use for a long period of time and the deterioration due to an atmospheric gas containing oxygen or humidity. Moreover, a light output of higher luminance, high conversion efficiency and the emission of blue, green and red light having high color purity are required under present circumstances in terms of applications such as a full-color display.
For example, Japanese Patent Application Laid-Open No. 2001-52868 discloses a diamine compound as a light-emitting material, but any emission of blue light with high color purity (chromaticity coordinates: x, y=0.14-0.15, 0.09-0.10) is not obtained. Japanese Patent Application Laid-Open No. H11-312587 discloses an example using a similar diamino backbone, but any emission of blue light with high color purity is not obtained.